Subtract.
Solution: There are many ways to solve this problem. Let's see two ways we can solve it. Place Value We can think in terms of tenths: $\begin{aligned} &\phantom{=}12-3.7\\\\ &=12.0-3.7\\\\ &=120\text{ tenths} - 37\text{ tenths}\\\\ &=83\text{ tenths}\\\\ &=8.3 \end{aligned}$ Place value table Let's line up the numbers by their decimal places. Tens Ones $.$ Tenths $1$ ${2}$ $.$ ${0}$ $3$ $.$ ${7}$ Now, let's subtract each place value column. Tens Ones $.$ Tenths $\overset{0}{\cancel{{1}}}$ $\overset{11}{\cancel{{2}}}$ $.$ $\overset{10}{\cancel{{0}}}$ $-$ ${3}$ $.$ ${7}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $\underline{~~~~}$ $8$ $.$ $3$ $8.3=12-3.7$